Various food products each require a varying degree of toasting in order to effect a desired "browness". For example, bread, muffins, crumpets and other food products each exhibit a varying degree of inherent untoasted browness, which inherent browness often results in excessive or inadequate toasting of the food product.
Conventional toasters perform adequately when set with respect to white bread but may over-toast brown bread and toasters which perform adequately when set with respect to brown bread may under-toast white bread. Compensation for the above may be effected by adjusting the toaster. This is often not precise and is often otherwise inconvenient or easily forgotton.
Furthermore, few toasters additionally incorporate a "warmup" feature, independent of a toasting function. Also, should the toaster be activated, without any food product therein, often hazardous toaster operation occurs, as a result of excessive heat.
U.S. Pat. No. 2,436,575 discloses a toaster which uses light emanating from a light source and reflected from toast, and measured either continuously or discontinuously, to produce a controlling current, which current operates a series of relays. When the current achieves a predetermined magnitude, the activated relays terminate the toasting operation. The specification also discloses a momentary delay operation to allow the photoelectric cell time to attain equilibrium when first measuring untoasted bread. U.S. Pat. No. 2,436,575 does not disclose a toaster wherein compensation for browness is effected dependent on the food product to be toasted.
U.S. Pat. No. 3,956,978 discloses a switching mechanism for a toaster to terminate supply of electricity to the toasting elements. This specification also discloses an alternative circuit which measures toast browness via light reflected from a separate light source in the toaster and also discloses a differential amplifier which triggers the termination of toasting when a desired browness is reached. However, the disclosed arrangement does not establish a signal which is needed to compensate for different bread types.
U.S. Pat. No. 4,363,957 discloses apparatus adapted to cook or char varied foodstuffs wherein the degree of charring is varied for each foodstuff. The control circuit described appears to generally disclose a circuit which stores a voltage representative of the maximum voltage provided by the optical sensor, that is minimum resistance of the sensor or maximum reflectively of the article, and uses this as a comparison datum in a comparator to compare changes or decreases in voltage as the article chars, to turn the power off at a certain changed level. U.S. Pat. No. 4,363,957 does not disclose the general concept of using a peak holding circuit to establish a reference representative of the maximum reflected light from the untoasted bread, measuring subsequent reflected light for the bread as it is being browned, comparing these results with a preset voltage representative of desired browning and terminating the toasting cycle when reaching the preset voltage in a toaster. The disclosure relies on a light source other than the toaster elements. The disclosure further does not teach a toaster having a timed warmup system, independent of the light sensor technique and also does not disclose a failsafe mechanism.
U.S. Pat. No. 4,426,572 relates to an improvement to U.S. Pat. No. 4,363,957. This disclosure deals with apparatus which more accurately measures light reflected from foodstuff being toasted. U.S. Pat. No. 4,433,232 relates to a further improvement to U.S. Pat. No. 4,363,957 and U.S. Pat. No. 4,426,572. This disclosure deals with the problem of accurately measuring the browness of foodstuff being browned, by avoiding the problem of light reflecting from the surface of the foodstuff.
U.S. Pat. No. 4,245,148 relates to a food browning device. The food browness is measured and dependent on surface colour. However, the specification does not disclose an apparatus which compensates its browness measurement according to the different types of foods being browned.
AU 66679/81 discloses a toaster which includes two light detectors, one arranged to monitor light emitted from a light source, the other arranged to monitor light reflected from an item being cooked. AU66679/81 does not disclose a toaster incorporating a warm-up feasture, nor a toaster which includes a failsafe feature. AU66679/81 does not disclose that the desired browness of various toasted foodstuffs is substantially equal when comparing the change in light reflected to a maximum amount of reflected light. The present invention is arranged to effect this.
DE 2,125,423 discloses a toaster which utilizes reflected light to measure the degree of brownness of toast irrespective of the type of bread being toasted or the moisture content thereof. With reference to FIG. 1, toast 3 is heated by electric element 1. Lights 5 and 51 reflect light from the toast to photocells 6 and 7. A mirror 15 is used to concentrate more radiant heat in area 19 on the toast than area 18. The desired degree of browness is measured by electronics 16 by comparing the brownness of areas 18 and 19. DE 2,125,423 does not disclose obtaining a maximum signal after which browness is measured, nor a warm-up feature.
DE 2,152,927 discloses a toaster which also utilizes reflected light to measure the degree of brownness of toast. However, it does not provide compensation for browning different types of bread, and accordingly, no maximum signal is derived after which brownness is measured. Furthermore, no warm-up feature or failsafe feature is disclosed.
JP,A, 57-198928 discloses a roaster wherein, with reference to FIG. 1, when toasting commences, capacitor 19 charges to level corresponding to a standard or the toast's initial reflectivity. After this switch 17 is switched over to begin browning of the bread, until the toast browness equals the value set on variable resistor 21. This specification does not provide a third signal, nor is there a disclosure as to what effects changeover of switch 17 to terminal "c", so that the toaster obtains a browness difference signal from the maximum value on capacitor 19. The present invention does not use a separate light source to irradiate the bread in the roaster, but uses the toasting elements to both radiated heat and enlighten the bread. The present invention also constantly senses the bread for a maximum light reflectivity, and so a more accurate assessment is made and a more consistent degree of browning is achieved between different types of toasted bread.
The present invention also uses one amplifier to initiate a maximum or peaking signal and provides or measures a difference signal. Use of one amplifier alleviates compensation and errors occurring as a result of more than one amplifier being used to measure and determine toast brownness.